Forgot your password?
typodupeerror

Comment: Re:Why so expensive (Score 1) 135

by HarvardAce (#43349707) Attached to: NASA Gets $75 Million For Europa Mission

So leaving the Solar System is less than twice as hard propulsion-wise as getting to orbit. Getting there in a timely fashion with working gear makes those sorts of problems harder. But merely being four orders of magnitude further away just isn't that big a deal. If you can get your stuff working in space in isolation for long periods of time, you have it.

How are you going to get the mass of the propellant into LEO? For every pound of payload (which in this case, includes the propellant to go from LEO to an escape trajectory from the solar system) it's something like 50 times as much propellant you need. So even if the propellant you needed was only 10% of what you needed to get into LEO, you would still need a launch vehicle that has 5 times as much propellant.

Hand-waving the time issue away is a big reach as well. Good luck getting anyone to spend a significant amount of money now for something that may pay off in 30-40 years.

Comment: Re:Missing mass of the universe? (Score 1) 77

by HarvardAce (#41181021) Attached to: NASA Uncovers Millions of New Black Holes

Perhaps someone knows... The more massive the gravitational field, the more time dilation, yes? The farther out you go the less drastic the effect is. Could the rotation just appear (to our frame of reference) to be moving not as fast in the middle (where the gravity is strongest) even though it is moving as it should according to our theories?

IINAP (and I'm guessing you're not, either). I used to think of things like this and say, "gosh, couldn't this be the explanation?" Then I remember that there are thousands of experts in the field, and it is extremely improbable that me, a layperson in the field, has thought of something -- especially something relatively (pun intended) simple -- that an expert hasn't thought of and obviously debunked (because we would have read about it were it plausible).

That said, I don't understand the physics behind gravity wells and their relation to time dilation very well, so I would be interested to hear from one of the aforementioned experts why it's not as simple as Taibhsear has made it sound!

Comment: Re:tau is wrong (Score 1) 241

by HarvardAce (#39331913) Attached to: Pi Day Is Coming — But Tau Day Is Better

Division is harder than multiplication. Given the choice between sometimes multiplying by 2, and sometimes dividing by two, we should pick the constant that forces the multiplication. Also, e^(pi * i) is nicer than e^((tau / 2) * i).

Hogwash! Multiply by 1/2 or divide by 1/2, and now the problem is reversed!

Comment: Re:22 light years (Score 1) 288

by HarvardAce (#38917349) Attached to: New Exoplanet Is Best Yet Candidate For Supporting Life

Since there is little friction in space what is there from stopping us from reaching an appreciable fraction of the speed of light? I was reading that we might attain lightspeed in about 1 year at 1G acceleration rate which only adds a couple of years to the trip..

Using force = mass * acceleration, energy = force * distance, distance = 1/2 * acceleration * time^2, and e=mc^2:
to accelerate a 1000kg payload at 1g (9.8m/s^2) for 1 year:
Energy to do so: 4.8 x 10^19 J
Equivalent mass of that energy: 532kg. That's also assuming Newtonian physics (no relativity), and not counting the fact that you have to account for the mass of the fuel. Let me know when we can produce 216kg of antimatter and then "burn" it in a controlled manner that directly corresponds to thrust.

If you use an energy density of 50,000 Wh/kg (very aggressive estimate of high-end energy density in current/near-future rocket tech), you're talking about needing over 2 billion metric tons of fuel (and don't forget you have to accelerate all that fuel too which now means you're no longer talking about a 1000kg payload.

Comment: Re:Raw- or OOP-base Lua? (Score 1) 145

by HarvardAce (#38893593) Attached to: Wikipedia Chooses Lua As Its New Template Language

True enough for people who run a website that mainly revolves around their wiki.

However, lots of people just throw a mediawiki install to supplement the rest of their site, usually precisely because it's dead simple to get running and works on just about any host. Moving to another host just to preserve their little 10 page wiki is probably not sensible, and the content is probably in-appropriate for external wiki hosts (or isn't desirable for other reasons).

Obviously for people with their own server (or in my case, a VPS) this is a non-issue .. but I figure there are probably enough people for which this would be an issue that I can't see them not at least providing a PHP only implementation as an option.

In your simple case, is there any reason to upgrade to a version of MW that implements LUA for templates, especially if it means an incompatibility with your current provider?

Comment: Re:Thats given me an idea... (Score 5, Informative) 416

by HarvardAce (#38763714) Attached to: What To Do With a 1,000 Foot Wrecked Cruise Ship?
$25M for a cruise ship? It cost 372 million pounds (or approximately $570M) to build in 2006. Aside from your order of magnitude, however, you have the right idea. It is quite probable that repairing the ship would be the most cost effective solution for the cruise line and its insurers.

Carnival's estimated financial impact factors in recovery and repairing of the ship rather than scrapping it, currently.

Comment: Re:The ratings agencies are worthless (Score 4, Informative) 1040

by HarvardAce (#37024294) Attached to: S&P's $2 Trillion Math Mistake

"All you need to know about rating agencies is that in May 2010 Moody’s still rated Greece triple-A." - Mark Steyn

I don't doubt that Mark Steyn said that, but what he said is false. In April 2010, Moody's lowered Greece's rating from A2 to A3, which is definitely not the same as Aaa. It is closer to "junk" rating than a triple-A rating. It is also worth noting that less than two months later, in June, Moody's cut the rating all the way to junk status, Ba1.

Comment: Re:Escape Velocity (Score 1) 208

by HarvardAce (#36828364) Attached to: NASA's Hubble Discovers Another Moon Around Pluto

Using Pluto's density of 2.03 g/cm^3, I compute (at 21 mile diameter) the moon is 4.2e16 kg.

With a 4.2e16 kg mass and 1.7e4 m radius, I compute an escape velocity of 18 m/s, or 40 miles per hour.

So I suspect you could jump really hard and not come back down, assuming I didn't misplace a decimal point.

I didn't double check your math, and you're obviously intentionally exaggerating the speed of a jump, but someone who could jump at 18m/s would have a vertical leap of about 16m or 50 feet on Earth.

Comment: Re:Let's lobby for a new standard (Score 1) 208

by HarvardAce (#36828022) Attached to: NASA's Hubble Discovers Another Moon Around Pluto

I thought there were still some stupid states that hadn't done that, or are you saying the last holdouts (I'm thinking PA was one) finally changing their exit numbering?

They haven't changed them here in CT or in nearby NY yet. There are, however gaps in the numbers sometimes...not sure if it's because the exits were removed, planned but never made, or someone didn't know how to count. For example, the first exit on I-95 in CT is exit 2.

Comment: Re:Godspeed Atlantis (Score 1) 275

by HarvardAce (#36698430) Attached to: Space Shuttle Atlantis Launches On Final Flight

In the short term it may just be a toy for the wealthy but there are profits to be made in space in the long term. The world's appetite for resources such as iron is increasing and there is a limited supply of it on this rock.

Yes, there is a limited supply of iron on Earth. There is also a limited supply of atoms on Earth, because the Earth is not infinite. However, iron is the most abundant element on Earth (source), although a good portion of that is in the Earth's core. The value of iron compared to the cost of mining it outside of our gravity well doesn't really add up, though. If mining iron outside of Earth ever becomes a profitable proposition then we're likely in dire straits already...

To understand a program you must become both the machine and the program.

Working...